Elevated and erratic blood sugar levels are components of the condition known as diabetes mellitus. This condition can be life-threatening and high glucose levels in blood plasma (hyperglycemia) can lead to a number of conditions caused by chronic diabetes, for example, atherosclerosis, microangiopathy, peripheral neuropathy, kidney disorders and renal failure, cardiac disease, diabetic retinopathy and other ocular disorders, including blindness. A precursor to diabetes, insulin resistance, may be a component in many age-related deteriorations and can result in alternating periods of both high and low blood sugar, uneven energy, obesity, hypertension and other disorders.
Diabetic conditions usually are treated medically in one of two ways. Insulin, the hormone which removes glucose from circulation, is supplied exogenously to treat the more severe cases in which the body's ability to produce this hormone is either impaired or nonexistent. Oral diabetes medications (such as sulphonylureas and biguanides) are also available. The drug metformin, a biguanide which is perhaps the safest and most successful of the usual oral hypoglycaemics, suppresses an elevated rate of basal hepatic glucose production. This mode of action in one of the more successful hypoglycaemic drugs underscores the fact that the inability to regulate and suppress hepatic glucose production is an important aspect of diabetes and prodiabetic conditions.
Momordica charantia Linn. (Cucurbitaceae), is commonly known as bitter melon, bitter gourd, karela, and pare. It grows in tropical areas of the Amazon, East Africa, Asia, India, South America, and the Caribbean and is used traditionally as both food and medicine. The plant is a climbing perennial with elongated fruit that resembles a warty gourd or cucumber. The unripe fruit is white or green in color and has a bitter taste that becomes more pronounced as the fruit ripens. The seeds, fruit, leaves, and root of the plant have been used in traditional medicine for microbial infections, sluggish digestion and intestinal gas, menstrual stimulation, wound healing, inflammation, fever reduction, hypertension, and as a laxative and emetic (Anonymous, 2007). Clinical conditions for which M. charantia extracts (primarily from the fruit) are currently being used include diabetes, dyslipidemia, microbial infections, and potentially as a cytotoxic agent for certain types of cancer (Oishi et al., 2007; Chaturvedi et al., 2004). An emerging body of evidence indicates that bitter melon in the form of non-hybridized or “wild” varieties exerts more powerful anti-diabetic effects than do modern cultivated varietals (Clouatre et al., 2011).
The primary constituents thought to be responsible for the hypoglycemic properties of M. charantia include charantin, insulin-like peptides, cucurbutanoids, momordicin, and oleanolic acids. M. charantia also has numerous other constituents including proteins, glycosides, saponins, and minerals (Ahmed et al., 2001; Harinantenaina et al., 2006; Clouatre et al., 2011). Extracts commonly are defined in terms of percentages of one or more of these active ingredients. However, controversy surrounds claims regarding the active principles of bitter melon. According to various authorities, the most prominent proposed active ingredients either have no clear quantitative relationship to physiologic effects or lack any worth for the treatment of blood sugar issues. For instance, some authorities deny that charantin exhibits any benefits whatsoever (Clouatre et al., 2011).
Bitter melon extracts also are notoriously unstable. The fresh fruit, the freshly expressed juice of the fruit, and freshly prepared extracts from the fresh fruit generally have been successful in animal and clinical trials. Nevertheless, prepared powdered extracts such as typically are characterized by charantin or bitters content seldom have demonstrated hypoglycemic efficacy.
The lack of efficacy of most prepared bitter melon extracts and the demonstrable unreliability of characterizations by the content of major constituents, such as charantin and bitters, in describing functional activity indicates a clear need for a reliable means of determining physiologic activity. Similarly, the instability of most extracts over time strongly indicates the need for a technique for quickly determining efficacy without having to resort to time-consuming and expensive animal or clinical trials at every point to determine potency. An in vitro test of functional efficacy is needed to allow for determining batch-by-batch performance and to improve upon the current extraordinarily spotty record of bitter melon extracts.